Fast time domain reflectometry (TDR) measurement approach for investigating the liquefaction of soils

Abstract

Time domain reflectometry (TDR) was used for the spatial observation of transient density changes in a laboratory shake-box apparatus. Shake-box experiments are conducted to investigate the liquefaction of soils due to seismic excitation. As a sensor, a flat ribbon cable was placed within a water saturated sand column two metres in height. In the experiment, the soil column was excited at its base with a sinusoidal signal with low frequencies and moderate amplitudes. During the tests, TDR measurements were conducted with a repetition rate of 30 s−1. Temporal density changes during the liquefaction and reconsolidation process of the quartz sand along the sensor could be shown through signal analysis. The mean porosities calculated from the relative dielectric permittivity using a soil-specific calibration function could be determined with an RMSD-value of 0.02 compared to the porosities determined from the height of the sample. With the metrological set-up for the TDR measurements being used, fast temporal changes in the density profile could be qualitatively visualized indicating the movement of the reconsolidation front during the liquefaction.